School of Pharmacy and Affiliated Hospital of Guiyang Medical University, Guiyang 550004, China.

Abstract

Cocaine use and relapse involves learned associations between cocaine-associated environmental contexts and discrete stimuli and cocaine effects. Initially, these contextual and discrete cues undergo memory consolidation after being paired with cocaine exposure. During abstinence, cocaine cue memories can undergo memory reconsolidation after cue exposure without the drug. We used a conditioned place preference (CPP) procedure in rats to study the role of neuronal protein kinase cyclin-dependent kinase 5 (Cdk5) in consolidation and reconsolidation of cocaine cue memories. We found that the expression of cocaine CPP in drug-free tests 1 d after CPP training (four pairings of 10 mg/kg cocaine with one context and four pairings of saline with a different context) increased Cdk5 activity, and levels of the Cdk5 activator p35 in basolateral but not central amygdala. We also found that basolateral (but not central) amygdala injections of the Cdk5 inhibitor beta-butyrolactone (100 ng/side) immediately (but not 6 h) after cocaine-context pairings during training prevented subsequent cocaine CPP expression. After training, acute basolateral (but not central) amygdala beta-butyrolactone injections immediately before testing prevented the expression of cocaine CPP; this effect was also observed on a second test performed 1 d later, suggesting an effect on reconsolidation of cocaine cue memories. In support, basolateral beta-butyrolactone injections, given immediately (but not 6 h) after a single exposure to the cocaine-paired context, prevented cocaine CPP expression 1 and 14 d after the injections. Results indicate that basolateral amygdala Cdk5 activity is critical for consolidation and reconsolidation of the memories of cocaine-associated environmental cues.

The expression of cocaine CPP is associated with increased Cdk5 activity and p35 protein levels but not Cdk5 protein levels in the BLA but not CeA. A, Timeline of the experiment (see Materials and Methods for the experimental conditions of the 4 groups). B, Mean ± SEM. CPP scores (time in the cocaine-paired minus time in the saline-paired side) during baseline preference and during a test for the expression of cocaine CPP 1 d after training. *Different from the other experimental groups, p < 0.05, n = 10 –15 per group. C, D, Cdk5 activity in the BLA and CeA; Cdk5 activity is expressed as specific counts (counts per minute). *Different from the other experimental groups, p < 0.05, n = 5–7 per group. E, F, p35 and Cdk5 levels in the BLA and CeA; p35 and Cdk5 levels are presented as a percentage (mean ± SEM) of values of naive control rats (n = 5). *Different from the other experimental groups, p < 0.05, n = 5– 8 per group.

Inhibition of Cdk5 in the BLA but not CeA prevents the consolidation of cocaine CPP. A, Timeline of the experiment. B, C, Mean ± SEM. CPP scores during baseline preference and during a test for the expression of cocaine CPP 1 d after training in rats injected with vehicle (0.5 μl/side) or β-butyrolactone (100 ng/side) into the BLA or CeA immediately after (0 min) or into the BLA 6 h after cocaine– context pairings (4 sessions) during CPP training. *Different from vehicle, p < 0.05. #Different from baseline, p < 0.05, n = 7–10 per group. D, p35 levels in the BLA and CeA in rats injected with vehicle or β-butyrolactone into the BLA or CeA immediately after the cocaine– context pairings during CPP training. *Different from vehicle, p < 0.05, n = 5–7 per group.

Inhibition of Cdk5 in the BLA but not CeA prevents the reconsolidation of cocaine CPP. A, Timeline of the experiment. B, C, Mean ± SEM. CPP scores during baseline preference and during tests for the expression of cocaine CPP in rats injected with vehicle (0.5 μl/side) or β-butyrolactone (100 ng/side) into the BLA or CeA immediately after (0 min) exposure to the cocaine-paired context on day 10 or into the BLA 6 h after context exposure. *Different from vehicle, p < 0.05, n = 7–10 per group.

Inhibition of Cdk5 in the BLA has no effect on reconsolidation of cocaine CPP when rats are not exposed to the cocaine-paired context before β-butyrolactone injections. A, Time-line of the experiment. B, Mean ± SEM. CPP scores during baseline preference and during tests for the expression of cocaine CPP in rats injected with vehicle (0.5 μl/side) or β-butyrolactone (100 ng/side) into the BLA on day 10 without exposure to the cocaine-paired context (n = 7–10 per group).

Additional characterization of inhibition of Cdk5 in the BLA on reconsolidation of cocaine CPP. A, Timeline of the experiment. B, Mean ± SEM. CPP scores during baseline preference and during tests for the expression of cocaine CPP in rats injected with vehicle (0.5 μl/side) or β-butyrolactone (100 ng/side) into the BLA or CeA immediately after (0 min) exposure to the cocaine-paired context on day 10. Five minutes before the last CPP test (termed cocaine priming in A), the rats were injected with cocaine (10 mg/kg, i.p.). *Different from vehicle, p < 0.05, n = 8 –10 per group.